Shifting C₂H₂/CO₂ Adsorption and Separation in Pillar‐Layered Metal–Organic Frameworks Finely‐Regulated by Molecular Rotation

Abstract

The efficient separation of C₂H₂/CO₂ mixture is crucial for industrial applications. A promising strategy is proposed herein to fine‐tune the C₂H₂/CO2 adsorption and separation by pillar‐layered metal–organic framework (MOF) adsorbents via molecular rotation. Keeping the same ultramicroporous architecture, three Zn‐X‐TRZ (TRZ = 1,2,4‐triazole) adsorbents are prepared with X‐pillar rotors varying from 9,10‐anthracenedicarboxylic acid (ADC), 1,4‐naphthalenedicarboxylic acid (NDC) to 1,4‐benzenedicarboxylic acid (BDC). Remarkably, the introduction of the largest ADC rotors enables Zn‐ADC‐TRZ with superior C₂H₂‐selective thermodynamic‐separation ability (highest heat of adsorption and IAST selectivity values) but poor dynamic‐separation performance caused by steric hindrance. Conversely, Zn‐BDC‐TRZ with the smallest rotors exhibit moderate CO₂‐selective thermodynamic‐separation ability, but excellent CO2/C₂H₂ dynamic‐separation ability with high‐purity C₂H₂ produced at 298 K (>99.5% obtained from 70% C₂H₂ mixture and >99.95% from 90% C₂H₂ mixture). In contrast, Zn‐NDC‐TRZ with medium NDC rotors shows comparable interactions and steric hindrance with C₂H₂ and CO₂, making both the thermodynamic and dynamic C₂H₂/CO₂ separation are unfavorable. Overall, controllable adsorption of C₂H₂ and CO2 is successfully achieved and shifted from C2H2‐selective to CO₂‐selective separation regulated by the pillared molecular rotation within pillar‐layered MOFs, providing a useful route for practical gas adsorbent exploration.